In the manufacture of a radial tire with equipment such as is used in current practice, it is common practice to first make a tire bead assembly which includes an inextensible bead core, an apex, and a gum tie strip. The edges of the gummed tie strip are turned up so that they abut the sides of the apex. An apparatus which includes an inflatable bladder is typically used for this purpose. The completed bead assembly in which the rubber is in the uncured state is then inserted into a tire onto a tire building machine. During tire building, the lateral edges of the carcass plies are turned up around the bead wires. An inflatable bladder, commonly known as a turnup bladder, is used to accomplish this. The rubbers forming the various tire components, including the carcass rubber and any rubber coating which surrounds the bead wires, are in the uncured or green state at this point in the manufacturing process. Turnup is typically carried out at ambient temperature (approximately 0.degree.-30.degree. C.).
A representative apparatus for forming a bead assembly, which apparatus includes an inflatable bladder for turning up the edges of the gum strip is shown, for example, in U.S. Pat. No. 4,163,683 to Lammlein.
A turnup bladder must be elastomeric in nature, i.e., it must have high elongation at break and must be capable of returning substantially to its original dimensions when stress is removed, since during its lifetime it will be subject to repeated inflation and deflation. In addition, turnup bladders should have high durability, good cut resistance, and the outside surface should have good release properties, so as to minimize or eliminate sticking of the uncured rubber of tire components to the outside surface of the turnup bladder. A bladder used in forming a tire bead assembly must also posses these characteristics.
A conventional turnup bladder comprises an outside layer of a polyurethane bonded to a base or core of a conventional diene rubber such as natural rubber (which is cis-1,4-polyisoprene), SBR (styrene-butadiene rubber) or a blend thereof. Other surface layer materials, such as polysiloxane having good release properties have also been suggested as a bladder material in U.S. Pat. No. 4,547,544 to Allardice.
Polyurethane-coated bladders have poorer release properties (i.e., greater adherence of uncured rubber to the polyurethane coating) and poorer cut resistance than what is desirable. Bladders made with other outer surface coating materials likewise have release properties and cut resistance which leaves something to be desired.